Humans have been applying tattoos to the skin for over 8000 years. The inks and dyes used were historically derived from substances found in nature and comprise a heterogeneous suspension of pigmented particles and other impurities. A well-known example is India ink, a suspension of carbon particles in a liquid.
Tattoos are produced by applying tattoo ink into the dermis, where the ink remains permanently. This technique introduces the pigment suspension through the skin by an alternating pressure-suction action caused by the elasticity of the skin in combination with the up-and-down movement of the needles. Water and other carriers for the pigment introduced into the skin diffuse through the tissues and are absorbed. The insoluble pigment particles are deposited in the dermis where initially placed, for the most part. Once the skin has healed, most pigment particles remain in the interstitial space of the tissue. Inks used for tattooing resist elimination by virtue of their inertness and the relatively large size of the insoluble pigment particles. A tattoo produced in this manner will partially fade over time and will generally remain present throughout the Life of the tattooed person.
Tattoos are used for a variety of reasons, primarily for ornamentation of the skin. While tattoos have traditionally been applied as designs for the skin, they are also used for permanent cosmetics, such as eyeliner and lip color often by people who cannot apply makeup, such as those suffering from arthritis or Parkinson's Disease. Additionally, for breast reconstruction after mastectomy, it is desirable to reconstruct the nipple and areola area with darker flesh tone tattooing in order to produce a natural-looking breast. Moreover, tattooing has been used to treat hypo- and hyperpigmentation caused by vitiligo, skin grafts, port-wine stains, and other dermatologic conditions.
In all types of conventional tattooing (decorative, cosmetic, and reconstructive), once the pigment or dye has been administered into the dermis to form a tattoo, the pigment or dye generally remains permanently in place. However, many people have a change of heart after being tattooed. For example, a person may desire to remove or change the design of a decorative tattoo. Alternatively, an individual with cosmetic tattooing, such as eyeliners, eyebrows, or lip coloring, may wish to change the color or area tattooed as fashion changes. In addition, following breast reconstruction, the geometry of the breast may change over time, leading to a tattooed nipple changing from an aesthetically pleasing position to an unpleasant one.
Unfortunately, there is currently no simple and successful way to remove tattoos. Removal by surgical excision, dermabrasion, or salabrasion requires invasive procedures associated with potential complications, such as infections, and usually results in conspicuous scarring. Removal by laser therapy is the most common technique and is usually limited to eliminating only from 50-70% of the tattoo pigment, resulting in a residual smudge. Laser removal requires multiple treatment sessions (usually five to twenty) with expensive equipment for maximal elimination. Thus, the overall cost of laser removal is generally prohibitively expensive.
Additionally, most tattooing inks are made of pigments which have a wide range of particle size. If the pigment particles are small, they may diffuse through the tissues, causing "bleeding" of the color, "blurring" of the lines of the tattoo, or partial fading of the tattoo.
Temporary substitutes for tattoos are unsatisfactory because they are very short-lived. If only the surface of the skin is colored, such as by a decalcomania-containing ink (henna tattoos) or by painting on the skin, the ornamentation is easily removed by wetting or rubbing the skin or by the natural sloughing of epidermis every three to four weeks. While this technique produces only temporary skin ornamentation, it would be desirable to have the option to color the skin to last longer than a few hours, days, or weeks.
Currently, the only other means to induce temporary color design on the skin is by selective tanning, such as disclosed in French patent 2,705,615 and German patent No. 3420867. However, unless the skin is repeatedly subjected to ultraviolet radiation to maintain the tan color of the skin, the color differentiation soon fades. Additionally, there is the danger of melanoma from exposure of the skin to ultraviolet light, and tanning is now highly discouraged.
There would be a significant advantage in being able to apply a stable, indefinitely lasting tattoo while still having the means to remove the tattoo on demand with a simple, non-invasive treatment which results in complete removal of the tattoo without scarring. In addition, it would be advantageous to have available for conventional tattoing a tattoo ink which did not become blurred or partially faded over time.